Xml DME hold function, is it even possible?

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Guest

HiI'm considering making a fully working DME unit, including a Hold function which displays the DME of the previously selected nav frequency. Emm, i.e. when the Nav frequency is changed or swapped, the DME stays tuned to the previous one. So far, I've only seen this feature in one single aircraft, so I guess that means this could be tricky to say the least.I believe Arne did this particular radio. How did you (or anyone else for that matter) do it? Like, I have no idea where to start, every brainstorming seem to hit the wall due to known limitations.

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Guest bartels

I have never tried it in XML, but what I did with the DME-HOLD function on a Cessna Centurion was, that the position of the tuned DME station is calculated each time the DME distance readout changes from bearing/distance to staiton and aircraft position. Then in the HOLD mode the distance to the previously logged DME position is calculated and displayed every 1 or 2 seconds, I can't recall exactly. So everything is simulated of course. I did calculate positions with sperical trigonometry just because I had the code lying around, in principle "flat" trigonometry with latitude correction should also work.If I observed it correctly there are positions available for the radio stations, but I don't know any conversions.I hope I could help you a bit.Arne Bartels

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Guest

>Hi >>I'm considering making a fully working DME unit, including a >Hold function which displays the DME of the previously >selected nav frequency. Emm, i.e. when the Nav frequency is >changed or swapped, the DME stays tuned to the previous one. >So far, I've only seen this feature in one single aircraft, >so I guess that means this could be tricky to say the least. >>I believe Arne did this particular radio. How did you (or >anyone else for that matter) do it? Like, I have no idea >where to start, every brainstorming seem to hit the wall due >to known limitations. Perhaps a kludge, but why not code it to 'temporarily' swap freqs on one of the NAV radios (you can recode the radio to NOT display the change), sample the DME, and then swap the NAV radio's freq again? You would only need to do this every five or six seconds to maintain a reasonable degree of accuracy on the DME readout (at least for light GA a/c!) A Concorde SST might be another case altogether! :)

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Guest

Arne: In the past I recall playing around with an A variable named stationlatlonalt or something like that (for different purposes), but all I could ever get out of that one was a big fat ugly zero - no data. Maybe it's busted in xml?Bill: One reasons, it would require "runtime" code (done "continously" or with a timer limit), which I have put my mind not to include more of as they slow down things too much, and there are way too many already. But I'm looking into it.

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